In the image input device and image input system as described above, for executing successive operations for imaging, it is necessary to read out image data and to store the read out data in a memory for each exposure, so that the time required to read out the data is different according to the number of pixels in a solid imaging element.
Especially, as a large number of pixels are set in a solid imaging element when a high-resolution image is to be obtained, a long time is required for reading out the data. And for this reason, in recent years, there has been proposed the pixel shift technique for achieving a higher resolution image with a smaller number of pixels.
Description is made herein of a conventional method of making a high resolution image. FIG. 13 is a timing chart for explaining a timing for pixel shift in an example based on the conventional technology, and FIG. 14 is a timing chart for explaining the pixel offset and a timing when an operation for imaging is executed in an enlarged dynamic range in an example based on the conventional technology.
At the timing for executing pixel shift shown in FIG. 13, a time for reading (TR) required for reading out image data from a CCD imaging element is set in a range, for instance, from 1/60 to 1/15 seconds, so that a time interval for releasing an electric shutter under the condition in which an exposure time in the first operation and in the second operation is set to a constant period of time, namely a time interval between timings each when an operation for reading out image data is started is obtained by adding a time for pixel shift (TS) to a time for reading (TR). The time for pixel shift (TS) is effected after the time (TF) for transferring charges from the photodiodes to the vertical CCD.
At the timing for executing pixel shift and an operation for imaging in an enlarged dynamic range shown in FIG. 14, a time interval between timings each when an operation for reading out image data is started is the same as that shown in FIG. 13, but by making an exposure time in the second operation for exposure (E2) different from that in the first operation for exposure (E1) (for instance, E1&lt;E2) for executing operations for imaging, the second image data can be used for some pixels which are out of a range to be exposed within a screen used in the first operation for imaging when the pixels are in an appropriate range in a screen used for the second operation for imaging. And for this reason, an image in a wide and dynamic range with a higher resolution can be obtained.
Further, description is made also of a method of obtaining a high resolution image when an all-pixels read-out type of CCD imaging element is not used. FIG. 15 is a timing chart showing a timing for reading out all pixels in a field read-out type of CCD imaging element according to an example based on the conventional technology.
In this example, in order to read out all pixels using the field read-out type of imaging element, a shutter mechanism which is an optical light-shuttering mechanism is used. At the timing shown in FIG. 15, the shutter mechanism is driven at the timing of generation of a mechanical-shutter signal after execution of the operation for imaging, and light to the CCD imaging element is shut. This light-shuttered state is continued until the operation for reading out the pixels is completed.
The operation for reading out pixels is executed twice in one operation for imaging, image data in an odd number of fields is read out in synchronism to a vertical synchronizing signal according to generation of a read-out signal R1 in a first operation for reading out pixels, and image data in an even number of fields is read out in synchronism to the vertical synchronizing signal according to generation of a read-out signal R2 in a second operation for reading out pixels.
It should be noted that a photodiode-control signal is generated after the read-out signals are outputted to remove electric charge accumulated in photodiodes (indicating sections in which a plurality of vertical lines are shown on the photodiode-control signal in FIG. 15). After the electric charge is removed from the photodiodes by means of this photodiode-control signal, the electronic shutter is actuated for exposure.
As described above, in the image input device and the image input system according to the example based on the conventional technology, the electronic shutter can be released to execute operations for imaging only at a time interval between the timings when the operation for reading out image data is started, which makes the device and the system inappropriate for imaging a dynamic object which requires high-speed successive operations for imaging and for imaging an object by a camera held in photographer's hands because these operations must be executed in consideration for shaking of the camera, and for this reason, imaging with the conventional device and system is limited to operations for imaging a still image of a static object, which does not allow full use of the imaging capability.
Nowadays, it has been proposed to use a plurality of sheets of CCD imaging elements and a prism for obtaining a high quality image without any time loss, but in that case the configuration is larger and complicated, and the cost is expensive, which is disadvantageous.